It is known to use optical light pipes or light guides including a semi-solid or solid optical fiber to transport light, as illustrated in U.S. Pat. Nos. 4,466,697; 4,422,719; and 3,641,332. Some such devices have included reflective sleeves surrounding the light transmitting fiber. For example, the inner surface of the sleeve could be formed with a reflective layer or a layer of material having a relatively low refractive index compared to that of the core, such as air, interposed between the sleeve and the core. However, a particular problem is that such devices do not easily lend themselves to transporting sufficient light for illumination because of the size necessary. In addition, utilization of such devices would be bulky and require a substantial amount of material, which would increase their weight and cost.
In addition, optical wave guides have been utilized to guide electro-magnetic wave energy, as illustrated in U.S. Pat. Nos. 4,453,803; 3,973,828; 3,583,786; 3,506,331; 3,436,141; and 3,386,043. Such devices include a sleeve portion or a hollow optical fiber. Similar to the optical light pipes or light guides described above, such devices have had a problem associated with the assembly and cost of the devices. Also, such devices are designed primarily to carry information for communication purposes in a single electromagnetic mode to increase the bandwidth of the information. This requires a highly specialized light source and optical system to properly direct quasi-monochromatic light into the device for propagation.
Further, a light guide made of a transparent material having substantially planar inner and outer surfaces which are "in octature" has been utilized to transport light, as illustrated in U.S. Pat. No. 4,260,220. This device is the most pertinent to the present invention. The device includes rigid polymeric sheets of a transparent material having a structured surface on one side and a smooth surface opposite the structured surface on the other side whereby light entering the light guide at an angle less than a predetermined maximum is totally internally reflected. However, a significant problem or limitation has been encountered with the use of such devices, namely the fact that it is restricted or constrained to a relatively small angular range of acceptable light rays. In addition, optical constraints require that the flatness of the sides be rigidly maintained in order to efficiently transport light material and labor costs associated with the assembly or construction of individual planar sections "in octature" to form such a rigid light guide are economic limitations.
The art as discussed above does not describe or disclose a hollow, tubular light conduit including a wall, of a transparent material, having a structured surface on one side and a smooth surface opposite the structured surface on the other side lying at least partially, in cross-section, in a smooth arcuate curve, which will achieve total internal reflection so that a predetermined portion of the light, incident within an acceptable angular range, is contained by total internal reflection for transporting and/or distributing the light. In addition, it does not describe a light conduit which because of its ability to totally internally reflect incident light within an acceptable angular range, may be utilized in light fixtures and lighting systems to transport and to distribute noncoherent, wideband solar light or artificial light for a variety of purposes. Also, the art does not describe a light conduit which is able to attain a variety of cross-sectional shapes with a portion of the wall lying in a smooth arcuate curve, while maintaining total internal reflection.